Adaptations Enabling the Move to Land

Transcription

1 Adaptations Enabling the Move to Land The movement onto land by ancestors provided unfiltered sun, more plentiful CO 2, nutrient-rich soil, and few herbivores or pathogens Land presented challenges: a scarcity of water and lack of structural support

2 Terrestrial plants are characterized by Chlorophylls a and b and carotenoids in their chloroplast Food stored as starch Cell walls of cellulose Sporic sexual reproduction involving an alternation of sporophyte and gametophyte generations

3 SPORIC SEXUAL REPRODUCTION

4 The Origin and Diversification of Plants Fossil evidence indicates that plants were on land at least 475 million years ago Fossilized spores and tissues have been extracted from 475-million-year-old rocks First land animal=428 million years ago

5 Those ancestral species gave rise to a vast diversity of modern plants Land plants can be informally grouped based on the presence or absence of vascular tissue Most plants have vascular tissue; these constitute the vascular plants Nonvascular plants are commonly called bryophytes

6 Seedless vascular plants Pterophytes (ferns and their relatives)

7 A seed is an embryo and nutrients surrounded by a protective coat Seed plants form a clade and can be divided into further clades: Gymnosperms, the naked seed plants, including the conifers Angiosperms, the flowering plants

8 Concept 29.2: Mosses and other nonvascular plants have life cycles dominated by gametophytes Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants: Liverworts, phylum Hepatophyta Mosses, phylum Bryophyta Mosses are most closely related to vascular plants

9 Key Bryophyte traits Lack vascular tissue Lack true leaves, roots, and leaves Gametophyte dominant life cycle

10 Bryophyte Gametophytes In all bryophyte phyla, gametophytes are larger and longer-living than sporophytes Sporophytes are typically present only part of the time

11 Multicellular Gametangia Gametes are produced within organs called gametangia Female gametangia, called archegonia, produce eggs and are the site of fertilization Male gametangia, called antheridia, are the site of sperm production and release

12 Bryophyta Life Cycle

13 A spore germinates into a gametophyte composed of a protonema and gameteproducing gametophore Rhizoids anchor gametophytes to substrate The height of gametophytes is constrained by lack of vascular tissues Mature gametophytes produce flagellated sperm in antheridia and an egg in each archegonium Sperm swim through a film of water to reach and fertilize the egg

14 Bryophyte Sporophytes Bryophyte sporophytes grow out of archegonia, and are the smallest and simplest sporophytes of all extant plant groups A sporophyte consists of a foot, a seta (stalk), and a sporangium, also called a capsule, which discharges spores through a peristome Hornwort and moss sporophytes have stomata for gas exchange

15 Fig. 29-9d Polytrichum commune, hairy-cap moss Capsule Seta Sporophyte (a sturdy plant that takes months to grow) Gametophyte

16 Traits of Vascular Plants Living vascular plants are characterized by: Life cycles with dominant sporophytes Vascular tissues called xylem and phloem Well-developed roots and leaves

17 Concept 29.3: Ferns and other seedless vascular plants were the first plants to grow tall Vascular tissue allowed these plants to grow tall WHAT IS AN ADVANTAGE OF HEIGHT? Seedless vascular plants have flagellated sperm and are usually restricted to moist environments

18 Pterophyta (Seedless Vascular plant) Key Traits Vascular tissue Sporophyte dominant Surface water required for sperm mobility

19 Pterophyta Life Cycle

20 Life Cycles with Dominant Sporophytes In contrast with bryophytes, sporophytes of seedless vascular plants are the larger generation, as in the familiar leafy fern The gametophytes are tiny plants that grow on or below the soil surface

21 Transport in Xylem and Phloem Vascular plants have two types of vascular tissue: xylem and phloem Xylem conducts most of the water and minerals and includes dead cells called tracheids Phloem consists of living cells and distributes sugars, amino acids, and other organic products Water-conducting cells are strengthened by lignin and provide structural support Increased height was an evolutionary advantage

22 Evolution of Roots Roots are organs that anchor vascular plants They enable vascular plants to absorb water and nutrients from the soil Roots may have evolved from subterranean stems What would water transport allow?

23 Plant can now get water easier and have support but how do they get away from needing a moist env.? Seeds Gymnosperm-exposed seeds Phylum Coniferophyta Angiosperms-enclosed seeds Phylum Anthophyta

24 Overview: Transforming the World Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems A seed consists of an embryo and nutrients surrounded by a protective coat

25 The Evolutionary Advantage of Seeds A seed develops from the whole ovule A seed is a sporophyte embryo, along with its food supply, packaged in a protective coat Seeds provide some evolutionary advantages over spores: They may remain dormant for days to years, until conditions are favorable for germination They may be transported long distances by wind or animals

26 Concept 30.1: Seeds and pollen grains are key adaptations for life on land In addition to seeds, the following are common to all seed plants Reduced gametophytes Ovules Pollen

27 Ovules and Production of Eggs An ovule consists of a megasporangium, megaspore, and one or more protective integuments Gymnosperm megaspores have one integument Angiosperm megaspores usually have two integuments

28 Pollen and Production of Sperm Microspores develop into pollen grains, which contain the male gametophytes Pollination is the transfer of pollen to the part of a seed plant containing the ovules Pollen eliminates the need for a film of water and can be dispersed great distances by air or animals If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule

29 Concept 30.2: Gymnosperms bear naked seeds, typically on cones The gymnosperms have naked seeds not enclosed by ovaries and consist of four phyla: Coniferophyta (conifers, such as pine, fir, and redwood)

30 Phylum Coniferophyta This phylum is by far the largest of the gymnosperm phyla Most conifers are evergreens and can carry out photosynthesis year round

31 The pine tree is the sporophyte and produces sporangia in male and female cones Small cones produce microspores called pollen grains, each of which contains a male gametophyte The familiar larger cones contain ovules, which produce megaspores that develop into female gametophytes It takes nearly three years from cone production to mature seed

32 The Life Cycle of a Pine: A Closer Look Three key features of the gymnosperm life cycle are: Dominance of the sporophyte generation Development of seeds from fertilized ovules The transfer of sperm to ovules by pollen

33 Coniferophyta Life Cycle

34 Characteristics of Angiosperms All angiosperms are classified in a single phylum, Anthophyta The name comes from the Greek anthos, flower Angiosperms are seed plants with reproductive structures called flowers and fruits They are the most widespread and diverse of all plants

35 Flowers The flower is an angiosperm structure specialized for sexual reproduction Many species are pollinated by insects or animals, while some species are windpollinated

36 Fig Stamen Anther Filament Stigma Pistil Style Ovary Petal Sepal Ovule

37 A pistil consists of an ovary at the base and a style leading up to a stigma, where pollen is received

38 Fruits A fruit typically consists of a mature ovary but can also include other flower parts Fruits protect seeds and aid in their dispersal Mature fruits can be either fleshy or dry

39 Fig Tomato Ruby grapefruit Nectarine Hazelnut Milkweed

40 Various fruit adaptations help disperse seeds Seeds can be carried by wind, water, or animals to new locations

41 A pollen grain that has landed on a stigma germinates and the pollen tube of the male gametophyte grows down to the ovary The ovule is entered by a pore called the micropyle Double fertilization occurs when the pollen tube discharges two sperm into the female gametophyte within an ovule

42 One sperm fertilizes the egg, while the other combines with two nuclei in the central cell of the female gametophyte and initiates development of food-storing endosperm The endosperm nourishes the developing embryo Within a seed, the embryo consists of a root and two seed leaves called cotyledons

43 Anthophyta Life Cycle

44 Assignments 1. All-Only Draw Antheridium and Archegonium 2. All-Antheridium and Archegonium can be drawn as on Prothallium for g 3. All-Only draw Mature pollen grains, Ovulate cone, Staminate cone 4. Only a,c,d,e,f 5. Omit